1. Field of the Invention
The present invention relates to a driving device for a vibration type actuator to be controlled by a periodic signal generating circuit of which frequency can be digitally adjusted in a small unit.
2. Related Background Art
The speed or the position of a vibration type actuator is controlled by the control of the driving frequency, and periodic signal generating circuits of following types are known for varying the driving frequency:
1) A periodic signal generating circuit disclosed in the U.S. Pat. No. 3,976,945 utilizes integra means and defining, as the delay amount, the time until the integration result by the integral means reaches a value set by D/A converting means thereby generating an arbitrary timing;
2) A periodic signal generating circuit disclosed in the Japanese Patent Application Laid-open No. 4-351008 utilizes a logic element as the delay element and generates an arbitrary timing by selecting an arbitrary number of delay elements, with such control that the total delay time coincides with the reference period;
3) A periodic signal generating circuit disclosed in the Japanese Patent Application Laid-open No. 2-184277 improves the resolution of frequency in pseudo manner by digitally switching the frequency dividing ratio at small intervals and meaning them.
The periodic signal generating circuit disclosed in the U.S. Pat. No. 3,976,945 is associated with a drawback that the desired timing is difficult to obtain unless the current supplied to the integral means is precisely controlled, and, in case of dividing a reference period, there may result a fluctuation in the number of division.
The periodic signal generating circuit disclosed in the Japanese Patent Application Laid-open No. 4-351008 is associated with a drawback that the number of the logic elements required for delay is basically equal to the number of division, so that there is required a vary large number of elements including the number of selecting means for selecting the delay amount.
Also in the periodic signal generating circuit disclosed in the Japanese Patent Application Laid-open No. 2-184277, as the resolution of the frequency is set in pseudo manner, the modulation component of frequency may fall in the audible range.